1. Field of the Invention
The present invention relates to the optics field, more particularly to transparent optical articles and preferably an ophthalmic lens, maintaining a mostly colorless appearance while comprising an optical filter intended to protect from blue light and optionally from UV light.
2. Description of Related Art
Visible light as perceived by humans approximately extends over a spectrum ranging from a 380 nm wavelength to a 780 nm wavelength. The part of this spectrum, ranging from around 380 nm to around 500 nm, does correspond to a high-energy, essentially blue light.
Many studies (see for example Kitchel E., “The effects of blue light on ocular health», Journal of Visual Impairment and Blindness Vol. 94, No. 6, 2000 or Glazer-Hockstein and al., Retina, Vol. 26, No. 1. pp. 1-4, 2006) suggest that blue light (around 430 nm) has phototoxic effects on human eye health, and especially on the retina.
Indeed, ocular photobiology studies (Algvere P. V. and al., “Age-Related Maculopathy and the Impact of the Blue Light Hazard», Acta Ophthalmo. Scand., Vol. 84, pp. 4-15, 2006) and clinical trials (Tomany S. C. and al., “Sunlight and the 10-Year Incidence of Age-Related Maculopathy. The Beaver Dam Eye Study», Arch Ophthalmol. Vol. 122. pp. 750-757, 2004) demonstrated that an excessively prolonged or intense exposure to blue light may induce severe ophthalmic diseases such as age-related macular degeneration (ARMD) or cataract.
Thus, it is recommended to limit the exposure to blue light potentially harmful, in particular as regards the wavelength band with an increased dangerousness (see especially Table B1, ISO 8980-3 standard:2003 (E) with reference to the B(λ) blue light dangerousness function).
To that end, it may be advisable for a spectacle wearer to wear before each of both eyes an ophthalmic lens which prevents or limits the phototoxic blue light transmission to the retina. Such lenses may also provide increased visual performance due to increased contrast sensitivity.
It has already been suggested, for example in the patent application WO 2008/024414, to cut at least partially the troublesome part of the blue light spectrum from 400 nm to 460 nm by means of lenses comprising a film partially inhibiting the light in the suitable wavelength range, through absorption or through reflection. This can also be done by incorporating a yellow dye into the optical element.
However, blocking blue light affects color balance, color vision if one looks through the optical device, and the color in which the optical device is perceived. Indeed, blue light-blocking optical devices incorporating a dye that at least partially inhibits light having a wavelength ranging from 400 to 460 nm appear yellow, brown or amber. This is esthetically unacceptable for many ophthalmic applications, and may interfere with the normal color perception of the user if the device is an ophthalmic lens.
Efforts have been made to compensate for the yellowing effect of conventional blue blocking filters. For example, blue blocking lenses have been treated with additional dyes, such as blue, red or green dyes, to offset the yellowing effect. However, this technique undesirably reduces the overall transmission of light wavelengths other than blue light wavelengths, which results in light attenuation for a lens user.
In view of the foregoing, there is a need for an optical article capable of at least partially blocking blue light that can further provide acceptable color cosmetics, i.e., that is perceived as mostly colorless by someone observing the optical article. Acceptable overall level of light transmission is also needed, as well as acceptable color perception for a user, i.e., the optical article should not impair dramatically the wearer's color vision in the case of an ophthalmic system. In particular, there is a need for an optical article that allows for selective blockage of wavelengths of blue light while at the same time transmitting at least 80% of visible light.
The present inventors discovered that optical brighteners, also called fluorescent whitening agents (FWA), optical brightening agents (OBA) or fluorescent brightening agents (FBA), could be used as a color balancing means, i.e., to minimize, and preferably eliminate, the change in color perception that results from blue-blocking by a blue light blocking dye incorporated into an optical system, as the blue light emitted by the optical brightener can compensate for the diminishing blue of the material treated by the dye and restore the original colorless appearance.
The present inventors also discovered that UV absorbers, which are frequently incorporated in optical articles substrates in order to reduce or prevent UV light from reaching the retina (in particular in ophthalmic lens materials), could interfere with the ability of optical brighteners to emit light by fluorescence. Therefore, a careful control of the respective locations of the blue light blocking dye, the UV absorber and the optical brightener is necessary to allow said optical brightener for efficiently balancing the color imparted by the dye, while not impairing the original UV blocking function of the optical article.